Project I will examine the neurobiological underpinnings of Attention- Deficit/Hyperactivity Disorder (ADHD), using functional magnetic resonance imaging (fMRI) to study children recruited in the initial Center program. Specifically, children initially assessed at 7.5-13.3 years will be systematically re-evaluated at ages 11-16 years. The sample and the significant progress made by our research group in using fMRI allow us to address four specific aims: 1. To determine the functional organization of the brain (using fMRI) in ADHD and within subgroups of ADHD (ADHD/IT, ADHD/CT), to determine whether particular brain activation patterns provide a "signature" for specific subgroups identified during the initial project period. 2. To determine the influence of comorbidity with RD on brain activation patterns (comparing ADHD without RD and ADHD with RD). 3. To determine the effects of pharmacotherapy on brain activation patterns: a) within subgroups of ADHD and b) between groups of children comorbid for ADHD and RD, i.e., ADHD without RD and ADHD with RD. 4. To relate brain activation patterns as determined with fMRI to changes in cognitive (particularly attentional and linguistic) processes comparing: a) ADHD with normals; b) within subgroups of ADHD (ADHD Inattentive vs ADHD combined type); c) ADHD with and without RD; d) effects of pharmacotherapy.